Seismic data can contain coherent noise signals, along with seismic reflection signals. Noise signals interfere with the interpretation of the seismic signals and have been suppressed during the processing of seismic data. Differences in the characteristics of coherent noise signals and seismic reflection signals have provided the basis for suppressing noise signals without also suppressing seismic reflection signals.
The suppression of coherent noise signals in a seismic section based on differences in trace-to-trace slopes between noise signals and seismic reflection signals is described by R. L. Sengbush and M. R. Foster in "Optimum Multichannel Velocity Filters," Geophysics, vol. 33, no. 1 (February 1968), pp. 11-35. Coherent noise signals and seismic reflection signals are described as often having overlapping frequency and wave length content, but having different ranges of trace-to-trace slopes. The use of multichannel filters is described for passing seismic reflection signals and rejecting coherent noise signals. This time-invariant approach for suppressing coherent noise signals is described as based on probability distributions for characteristics of the coherent noise signals and the seismic reflection signals.
The time-invariant use of optimum multichannel seismic data filters is described by E. Cassano and F. Rocca in "After-Stack Multichannel Filters Without Mixing Effects," vol. 22, Geophysical Prospecting (1974), pp. 330-344. It is described that superior results are achieved by assuming that signal components contained in different traces are independent from each other and that the multichannel filters are required to have a sufficient number of channels to suppress coherent noise signals when their trace-to-trace slopes are close to the trace-to-trace slopes for seismic reflection signals in the low frequency region.
These filters are referred to as velocity filters and as dip filters. When they are constructed for considering changes in time over space, they are referred to as dip filters. When they are constructed for considering changes in space over time, they are referred to as velocity filters.
It has now been discovered that these time-in-variant filters can be used by a seismic data analyst in a time-variant manner for suppressing coherent noise signals in selected portions of seismic sections. The time-in-variant use of these filters can result in the suppression of seismic reflection signals, along with coherent linear noise signals when the seismic reflection signals have similar characteristics to the noise signals that are being suppressed.